feat(theme): add catppuccin themes with transparency and 256-color support

Add a theme package providing all four catppuccin flavors (mocha,
frappe, macchiato, latte) mapped to the xterm-256 palette. Themes are
selected with -theme or the CTOP_THEME environment variable; -i inverts
the flavor. Background slots use the terminal's native color for
transparency (opt out with -solid / CTOP_SOLID), and termbox is switched
to Output256 so colors render correctly. Replace hardcoded colors in the
compact and single views with ctheme portrait slots.

widgets/menu/main.go

@@ -3,6 +3,7 @@ package menu
 import (
 	"sort"
 
+	"github.com/bcicen/ctop/theme"
 	ui "github.com/gizak/termui"
 )
 
@@ -105,7 +106,7 @@ func (m *Menu) Buffer() ui.Buffer {
 		for _, ch := range item.Text() {
 			// invert bg/fg colors on currently selected row
 			if m.Selectable && n == m.cursorPos {
-				cell = ui.Cell{Ch: ch, Fg: ui.ColorBlack, Bg: m.TextFgColor}
+				cell = ui.Cell{Ch: ch, Fg: theme.Attr("crust"), Bg: m.TextFgColor}
 			} else {
 				cell = ui.Cell{Ch: ch, Fg: m.TextFgColor, Bg: m.TextBgColor}
 			}